Pack carburizing with furane derivatives



United States Patent PACK CARBURIZING WITH FURANE DERIVATIVES Gerhard W. Ahrens, Brooklyn, N.Y.

No Drawing. Original application May 29, 1948, Ser. No. 30,220. Divided and this application Feb. 21, 1958, Ser. No. 716,563

6 Claims. (Cl. 148-16.S

This invention relates to the case hardening of metals such as iron and steel, and carburizing agent therefor.

This is a continuation in part of my application under Serial Number 266,116, filed January 11, 1952, now abandoned, entitled Metal Hardening with a Furane Derivative, a division of Serial Number 30,220, filed May I 29, 1948, now abandoned, entitled Electrolytes for the Treatment of Metals and for Deposit Formation of Metals and Alloys.

My novel process utilizes furane derivatives as carburizing agent possessing a relatively highly reactive carbonyl group in a readily substituted -position with mono-atomic oxygen on conjugated double bonds. These furane derivatives may be employed in their adsorbed condition to a carrier material that permits repeated regeneration and can be reused after readsorption of new furane derivative has been permitted.

The usefulness of furane derivatives for carburizing resides in the fact that it forms a rich prolific source of carbon monoxide which can be procured by means of heating the furane derivative, for instance by heating furan to a temperature of 670 C., or by heating furan to a temperature of 360 C. in the presence of a decomposition catalyst for the same such as nickel or nickelous acetate, or cobalt or cobaltous acetate, causing I the formation of at least 75% by weight carbon monoxide as the main product of decomposition together with residual gases also beneficial for carburizing such as hydrogen, acetylene and other hydrocarbons.

In the carburizing of steel, for example, the steel article may be packed in a solid carburizing compound material contained in a carburizing pot or box of a suitable size, which is thereafter sealed with clay and introduced into a suitable treating furnace, for instance, a pusher type heating furnace and therein heated to requisite temperature appropriate of the desired depth of carbon case on a particular type of steel used for the steel article being treated for periods of time appropriate thereto. In order to cause the carburizing of the steel, it is essential that carbon monoxide be present or formed which diffuses into the structure of the outer section of the steel, decomposing in contact therewith, due to the catalytic action of the iron in the steel, and setting free nascent carbon which is deposited thereby. The reaction may 'be described as being of the order: 2CO' '*CO +C. The carburizing eifect thus depends upon the presence of carbon in the nascent state and, therefore, as already pointed out, upon the presence of active carbon monoxide to be decomposed. The actions involved are of the order: 3Fe+2CO Fe C+CO The more carbon monoxide can be concentrated in immediate contact with the steel surface and at this surface, the greater will be the amount of Fe C formed which is then forced to 'migrate, upon continued heating, into the inner structhe primary carburizing agent.

Patented Aug. 9, 1960 ture of the steel, even without further additions of carbon monoxide. There is no soot formation if the carburization is carried out with carbon monoxide as reactant with the iron, making it particularly desirable to have available at the time when carburization commences as great amounts of carbon monoxide as possible to act as 7 If furane derivatives are decomposed by heating, particularly in the presence of a decomposition catalyst for the same, carbon monoxide is surprisingly richly' and speedily supplied for use as carburizing agents in accordance with this invention and on account of the fact that all furane derivative used with this invention form carbon monoxideupon decomposition as the major end product thereof and in prolific amounts even before reaching actual carburizing temperatures during the carburization of iron and steel.

In carrying out the carburizing reactions of this invention, there may be used a carburizing compound containing carbonaceous material together with or without energizers to which is added a furane derivative together with or without catalyst for the decomposition of said furane derivative and with or without the presence of carburizing accelerating agents for the iron or steel being treated, and the addition to the carburizing compound .the nascent carbon for energizing reactions. hydroxide initiates similar reactions, and the-final result of carbonates is carbon dioxide formation, nascent oxy;

containing carbonaceous material is accomplished by the simple procedure of adsorption thereto, followed by dry.-

ing. The resulting carburizing material possesses a booster-like, highly reactive and enhanced supply of carbonmonoxide forming constituents. As heating to carburizing temperatures causes carburizing reactions to take place, the extra booster charge of the co-present furane derivative in the carburizing compound containing carfore carburizing temperatures can be reached, which is beneficial because the article to be carburized will be exposed to large amounts of carbon monoxide,.which is an extremely stable gas at high temperatures, permitting such large amounts of carbon monoxide to be present at the moment carburizing temperatures have beenreached that the pressure from this gas acts to accelerate carburization and initiate carburization before suflicient carburizing gas can be produced by the standard carburizing compound to which the furane derivative had been added. The catalyst material, eg, nickelous acetate, which also decomposes under the action of heat, acts like- -Wise, to enhance the supply of carburizing gas and decomposes to form nascent oxygen at 1,112 E, which reacts at once with carbon dioxide that is present to form more carbon monoxide, whilst the ionic nickel is retained upon the body of the carbonaceous material of the carburizing compound to continue its catalytic effects. If an energizer is present such as potassium hydroxide or sodium hydroxide, or potassium carbonate or sodium carbonate, thesame will react with the carbon, for example, in the case of potassium hydroxide, to form potassium cyanide, as the nitrogen that is derived from occluded air in the charge is being utilized together with Sodium gen formation and cyanide formation to boost carburization reactions. If, in addition to the catalyst, a carburization accelerating agent is used, such as chromous acetate, molybdic acid, manganous acetate, manganese trioxide or manganous heptoxide, the carburizing reaction at the metal interface is speeded up very considerably because elements of this group, e.g. chromium, molybdenum and manganese are known to accelerate carbon deposition in a steel structure, so that their use in conjunction with the use of a furane derivative as a prolific source of carbon monoxide acts to enhance the speed with which carburization in a steel takes place.

In the carburization reactions of this invention may be employed also inert adsorbent carrier materials, for instance, a ceramic material such as activated alumina, coke or charcoal in the form of pellets, balls, pearls and other comminuted shapes of pieces thereof that possess good structural strengths and are of a size averaging between from A inch and inch in diameters and to these inert carrier materials is a furane derivative adsorbed, whereby such furane derivative constitutes the sole active source for carburizing gas needed in carburizing reactions which is replenishable with respect to the inert carrier material which can be, after being depleted through use, readsorbed by a new charge of carburizing agent and again be ready for use, thereby effecting considerable savings in the costs of carburizing materials for use in carburizing operations. This feature of reusefulness of the carrier material for the carburizing agent of the invention enables also the employment of otherwise too expensive materials as carrier materials, e.g. of the above mentioned activated alumina and utilizes the superior adsorption properties thereof for furane derivatives, e.g. for furfural which is adsorbed to activated alumina at the rate of 41 parts by weight of alumina and represents a totally unexpected result in view of the fact that only from 4 to 5 parts by Weight of benzene can be adsorbed to activated alumina or parts of water by weight of alumina at 90 F. or 12 parts of oil by weight of alumina. Thus, the high adsorption of furfural constitutes an unexpected phenomenon, which is also extended to the use of charcoal to which 23 parts by weight thereof can be adsorbed and to coke to which 13 parts by weight thereof can be adsorbed. This being so, it appears to be an important property of furane derivatives to pass into porous bodies to permit the utilization of low-priced coke and charcoal for use as carrier materials for these furane derivatives, e.g. furfural, as the same is being held adsorbed to the structure of said carrier materials in the same way as to the structure of the above described ceramic carrier materials, utilizing thereby important characteristics of said carrier materials that make the same ideally suited as supporting means also for steel articles during carburization thereof and minimizing warpage and deformations in such steel articles by virtue of their inertness, rigidity, stability, infusibility and low shrinkages which they suffer even under severe carburizing conditions. Another welcome feature is exhibited by coke as it is utilized as a carrier material for a furane derivative serving as carburizing agent for a steel article, in which the high thermal conductivity of coke provides for close uniformity of heating the charge and, consequently, assures uniformity in the carburized case obtainable for a given type of steel from which the steel article has been made.

Using inert carrier materials, it shall be within the scope of this invention to add, if deemed desirable, energizing agents to the charge, e.g. water soluble carbonates or hydroxides of the alkali metals, sodium or potassium, such as sodium hydroxide or potassium hydroxide, or sodium carbonate or potassium carbonate, in conjunction with a furane derivative as carburizing agent. The adsorption of such energizing agent to the carrier material may preferably be carried out through first preparing .4 an aqueous solution of said energizing agent, then permitting the same to be adsorbed to the carrier material and drying thereafter, and finally permitting the adsorption of the furane derivative to the carrier material containing the energizing agent. It shall also be within the scope of this invention to add, if desired, a catalyst for the furane derivative decomposition, e.g. nickelous acetate or cobaltous acetate, to the carrier material for the furane derivative, and the adsorption thereof to the carrier material may be carried out by preparing an aqueous solution of the catalyst which is adsorbed to the carrier material and dried thereafter, followed by the final adsorption of the furane derivative, and where an energizer as well as a catalyst is a desirable constituent for the carrier mate: rial, together with a furane derivative, both the energizer and the catalyst may be adsorbed to the carrier material from their aqueous solutions, dried together with the carrier material, and then the final adsorption of the furane derivative to the carrier material performed. In addition, it shall be also within the scope of this invention to add, if deemed desirable, carburizing accelerating agents to the charge, e.g. chromous acetate, molybdic acid, manganese acetate, manganous trioxide or manganese heptoxide, in conjunction with a furane derivative as carburizing agent, whereby the carburizing accelerating agent may preferably be dissolved in water and then permitted to be adsorbed to the carrier material, followed by drying and final adsorption of the furane derivative; and where there is desired such carburizing accelerating agent in a charge together with energizers and catalysts for the furane derivative decomposition and furane derivatives, each of these materials may be separately permitted to be adsorbed before the final adsorption of the furane derivative to the carrier material is carried out.

As is the prime function of energizers to produce carbon dioxide which reacts with nascent carbon to increase the supply of carbon monoxide during carburizing operations, and also to liberate other gases that might be able to reduce carbon dioxide to carbon monoxide, the carburizing agent of this invention, which is a furane derivative and which constitutes-inter alia-by its reactivity characteristics a prolific source of carbon monoxide under decomposition conditions under heat application, is capable of completely substituting these energizers and permits the use thereof as self-energizing carburizing material and in conjunction with carburizing compounds deplete of added energizers.

It is desirable to subject low carbon steels and low alloy steels to case hardening by carburizing, for instance, where a medium case depth of from .04 to .06 inch carbon penetration into the surface of the steel might be desirable, such as in articles like gears and where a high wear and crush resistance as well as a high resistance to alternating bending stress is required. In addition, where heavier cases of more than .06 inch carbon penetration into the surface of the steel are desired, same are almost entirely procured by means of carburizing reactions carried out in carburizing pots or boxes placed in furnaces adapted therefor and treated therein by heating to temperatures appropriate to the type of steel used, and desired carbon penetration therein, which is ruled by the time periods used for the heat treatment under carburizing conditions and the temperatures applied during the heat treatment periods under carburizing conditions.

Among low carbon and low alloy steels, of which the former shall preferably contain from .15% to .25% carbon and .45 manganese aside of a low sulfur and phosphorus content; and of which the latter shall preferably contain from .15% to .40% carbon and from .95% to 5.85% of alloying metals in addition to from .45% to .65% manganese aside of a low sulfur and phosphorus content, are:

Steels oft'he following composition representative of useful carburizing steels:

Percentages of representagve elements therein aside of on Glass-Type Mn P S Si Ni 01' Mo V S..A.E. .45 .045 .055

S.A.E. 10 .45 .045 .055

S.A.E. 10 .46 .045 .055

S.A.E. 231 .45 .040 .050 .20 3. 50

S.A.E. 232 .45 .040 .050 20 3. 50

S.A.E. 25 .45 .040 .050 20 5. 00

Low N -Gr 45 .040 .050 20 65 S.A.E. 3115..... 45 .040 .050 1.

Low Nl-Or-Mo- 20 .45 .040 .050 .20 1.25

S.A.E. 3215..... 15 .45 .040 .050 20 1. 75

S.A.E. 3325..... 25 .45 040 050 .20 3. 50

Low Or-Mo.-.- 20 .45 .040 .050 20 S.A.E. 4615..... 15 .55 .040 .050 20 1. 80

S.A.E. 4640.--.. 40 .65 .040 .050 20 1.80

S.A.E. 5120.--.. 20 .45 .040 .050 20 S.A.E. 6120.---. 20 .45 .040 .050 20 The invention may employ as furane derivative furan, furfural, furfuryl alcohol, furfuryl acetate and furoic acid, which latter, being a solid, may be used in aqueous solutions to cause adsorption to carrier material, whereas the others, being liquids, require no diluents for their successful adsorption to carrier material. It shall also be understood that, for the purposes of this invention, the furane derivative employed may constitute a mixture of at least two furane derivatives, such as furfural with furfuryl alcohol; furfuryl acetate with furfural; furfural with furan; furoic acid with furfural; furfuryl alcohol with furfuryl acetate and furan or furfural with furfuryl alcohol and furan, or the furane derivatives may be employed interchangeably, if desired, whereby their common characteristic of high penetrability into porous substances serving as carrier material is utilized and imparts thereby to the carrier material increased active usefulness, e.g. in the case of active alumina the adsorption of better than 40 parts by weight of the alumina of furfural, whereas water at a temperature of 90 F. is adsorbed to activated alumina only at the rate of 10 parts by weight of the alumina and benzene also only at a rate of from 4 to 5 parts by Weight of the alumina and oil at the rate of no more than a limiting 12 parts by weight of alumina.

The invention makes use of adsorbent carrier materials for furane derivatives as carburizing agents and these carrier materials may or may not be carbonaceous in origin and may or may not possess carburizing properties. The invention may make use of carburizing compounds containing carbonaceous material of an adsorbent character and adsorbing to such a material a furane derivative as co-carburizing agent and booster for the charge contained in the carburizing compound. The invention also makes use of ceramic carrier materials as preferred carriers for the carburizing agent of the invention because of the great economic advantage uttered by the reusefulness of ceramic carrier materials. Too, the invention makes use of charcoal as the inert carrier material for the highly reactive carburizing agent of the invention adsorbed to the surface and into the inner structure of such charcoal carrier, thereby not relying on the carburizing activity which such charcoal might possess and which is lost rapidly after first being used, whereas the charcoal in its deactivated state also permits reuse as carrier material for a new charge of carburizing agent of the invention at great economical advantage. The invention makes, in addition, use of coke as the adsorbent inert carrier material for the highly reactive carburizing agent of the invention which is adsorbed into the structure of this carrier material to an unexpectedly high degree and is held therein adsorbed to make use of the preferred physical characteristic of coke, e.g. the high heat conductivity which permits uniform heating of a 'charge and the infusibility of coke which avoids fusing 6. to met'al'parts being'treated while they are in close contact with the coke which supports the weight of such metal parts under treatment and the stability andinertness of coke which avoids any chance of side reactions taking place during the carburizing treatment and also the smokelessness of coke at high temperatures which avoids soot formation so detrimental to carburizing operations and finally the non-shrinking quality of coke which minimize any possible deformations and warpages in steel articles during carburizing operations. In addition, coke is very economical as it provides still another carrier for the carburizing agent of the invention that can be reused after each use and depletion by the simple provision of readsorbing to the dry coke that had been recovered a new charge of carburizing agent, thus constituting a great economical advantage also in conjunction with its ready availability at low costs.

The relationship between the constituent parts forming the carburizing material of the invention may be as follows: If the carburizing agent is to be added to a carburizing compound containing carbonaceous material, the amount of adsorbed carburizing agent of the invention shall be from 5 to 23 parts by weight of the carburizing compound containing carbonaceous material. If the carburizing agent of the invention is to be adsorbed to a ceramic carrier material, e.g. activated alumina, the amount of carburizing agent shall be from 35 to 41 parts by weight ofthe activated alumina. If the carburizing agent of the invention is added for adsorption to charcoal as the inert carrier material, the amount of the carburizing agent shall be from 15 to 23 parts by Weight of the charcoal, and if the carburizing agent of the invention is to be added to coke as the inert carrier material, the amount of adsorbed carburizing agent shall be from 8 to 13 parts by weight of the coke. If in addition to the carburizing agent also energizers are employed together with carburizing agent of the invention, the amount thereof shall be from 1 to 5 parts by weight of the carrier material employed therein containing the carburizing agent of the invention, andif, in addition to energizers, catalysts for the decomposition of the carburizing agent of the invention are added, the amount of these catalysts shall be from .3 to 1.5 parts by weight of the employed carrier material therein, and if these catalysts are added without the presence of energizers,

the amounts thereof shall be from 0.2 part to 1.5 parts by weight of the employed carrier material. If now, in addition to energizers, carburization accelerating agents are added to the carrier material containing the carburizing agent of the invention, the amount thereof shall be from 0.1 part to 1.5 parts by weight of the carrier material employed and if it is desirable to add catalysts in addition to the presence of energizers, the amounts thereof shall be from 0.1 to 1.5 parts by weight of the carrier material; and where it is desired to add only carburization accelerating agents together with catalysts to the carrier material in conjunction with the carburizing agent of the invention, without the presence of energizers, the amount thereof shall be from 0.1 to 1.5 parts by weight of carburizing accelerating agents together with from 0.1 to 1.5 parts by weight of the catalysts by weight of carrier material.

In order to illustrate the invention more clearly, the following are examples:

EXAMPLE 1 The carburizing compound in this example is prepared by mixing 1000 lbs. of charcoal of a suitable pellet size, preferably powdered, with 50 lbs. of potassium hy- 1A inch and inch average diameter and thereafter dried and permitted to adsorb lbs. offurfural; 'The resulting material is a highly reactive booster-type novel carburizing agent with superior carburizing activity. A steel article made of low carbon steel and of the size 8 inches long, -6 inches wide and inches thick may be placed into a carburizing pot of one cubic foot capacity together with this carburizing agent for supporting the article during the carburizing procedure that is to follow. About 35 lbs. of the carburizing material are packed about and around the steel article in the way generally known in the art and the carburizing pot closed with its cover and the seams luted with clay. The carburizing pot with its readied charge is now introduced into a suitable temperature-controlled heating furnace, for instance, of the pusher type and heated therein to the temperature appropriate for low carbon steel, e.g. to 1640 F. for times appropriate to obtain the desired case depth of carbon penetration into the surface of the steel under treatment, e.g. 4 hours, to obtain a one millimeter case depth. After cooling the furnace down to about 1325" F., the carburizing box is removed from the furnace, opened and the steel article subjected to further treatments not within the scope of this invention, e.g. quenching or the like. It is to be noted that the carburizing charge has been primarily supplied from the decomposing furane derivative furfural, which permitted the reduction in energizers and carburization accelerators in the charge, in which usually are present at least to energizers and up to 5% carburization accelerators. After removal of the steel article from the carburizing pot, the carburizing material that is still presem; and exhausted of its active charge, except for its content of nickel and residual manganese derived from decomposition of the originally present nickelous acetate and manganous acetate, can be reused by being permitted to be readsorbed with another charge of furfural.

EXAMPLE 2 Inert ceramic carrier As another example, carburizing material adsorbed to an inert ceramic carrier material is prepared by utilizing activated alumina, preferably in form of pebbles or balls of a size averaging between inch to inch in diameter. Thus, 100 lbs. of activated alumina in the form of balls or pebbles are permitted to adsorb 10 lbs. of a 15% solution of nickel acetate in water, followed by drying. The dry material is then permitted to adsorb a further charge of 10 lbs. of a 50% solution of potassium carbonate in water and dried hereafter, and this is followed by the adsorption of a 3% solution of molybdic acid in water at a temperature of 80 C. and employing '5 lbs. of this solution and the temperature being not an essential feature except for the higher solubility of molybdic acid at this temperature in water. After the adsorbed carrier is again dried, the final adsorption of 35 lbs. of furfural to the carrier material is carried out under cooling the container in which the adsorption takes place, and the resulting carburizing material is ready for use. A steel article made of low carbon steel and possessing the dimension of 8 inches in length, 6 inches in width and being of 5 inches thickness may be placed into a carburizing pot of one cubic foot capacity together with the carburizing material in the form of balls of inch diameter, which act to support the steel article during the carburizing operation to minimize warpage and distortion in the latter. After packing the carburizing material around and about the steel article, which re quired a charge of 40 lbs. carburizing material, the carburizing pot is closed and sealed with clay and then introduced into a pusher type heating furnace that is heat-controlled and heated therein to a temperature of 1640 F. for a period of time appropriate to obtain the desired depth of carbon case in the surface of the steel, e.g. 4 hours to obtain a case depth of one millimeter. After cooling the furnace to about 1325 F., the carburizing box is removed from the furnace, opened and the steel article removed therefrom to be subjected to further treatments not within the scope of this invention, e.g. quenching, whereas the depleted carburizing material is again subjected to another adsorption of furfural and thereafter again ready for use. The recovered charge of 40 lbs. has lost weight on account of furfural losses from decomposition during carburizing and these losses amount to from 10 to 12 lbs., which is the charge necessary to be replenished for reuse of the carburizing car- 'rier material. Thus, to the recovered carrier material weighing 28 lbs. to 30 lbs. are added 12 to 10 lbs. of fresh furfural to result in a reusable carburizing material.

EXAMPLE 3 As a further example, the carburizing material may consist of inert coke as carrier for the adsorption of the carburizing agent that is represented by a furane derivative. Thus, to lbs. of coke in the form of pebbles or particles having an average diameter of from /4- inch, e.g. pea-coke, for example, are adsorbed 5 lbs. of a 15% nickelous acetate solution and thereafter dried. This is followed by adsorption of 5 lbs' of a 40% solution of potassium carbonate in water and again drying before a third adsorption of 5 lbs. of a 2% solution of molybdic acid in hot water is facilitated and again dried for the final adsorption of 10 lbs. of furfural to the coke which is thereafter ready for use. A steel article of a low carbon steel measuring 8 inches in length, 4 inches in width and 6 inches in thickness may be placed into a carburizing box having a capacity of 1 cubic foot together with the pea coke material containing carburizing agent adsorbed thereto, and which is packed about and around the steel article, therefor requiring a charge of 30 lbs. of this pea coke material. After closing the carburizing box and luting the same with clay, same is introduced into a suitable heat treating furnace, e.g. a pusher type furnace and heated therein to a temperature of 1 640 F. for a period of time which causes a case depth of carbon to be formed of 1 millimeter penetration into the steel surface of the steel article being carburized, e.g. by heating for 4 hours. This is followed by cooling to about 1325 F., removing the carburizing box from the furnace, opening the same and removing the carburized steel article from the same for further treatment which is not within the scope of this invention, e.g. for quenching, whereas the depleted coke is removed and readsorbed with a new charge of furane derivative to be readied for reuse. To the depleted coke are added 3 lbs. of furfural for readsorption, equivalent to the lost charge during carburizing operations.

EXAMPLE 4 As a still further example, the carburizing material may consist of a standard grade charcoal as carrier material for the adsorption charge of the carburizing agent supplemented by a furane derivative. Thus, to 100 lbs.

of charcoal in the form of pellets averaging in size from inch to inch in diameter are adsorbed 10 lbs. of a 15% solution of nickel acetate in water and dried, leaving, after drying a charge of 1.5 lbs. of nickel acetate in the structure of the charcoal. This is followed by the adsorption of 10 lbs. of a 50% sodium carbonate solution in water and drying to leave a charge of 5 lbs. of sodium carbonate in the structure of the charcoal in addition to the 1.5 lbs. of nickel acetate and this is then followed by permitting the adsorption of 3 lbs. of a 10% solution of manganous acetate in water, followed again by drying and permitting a charge of .3 lb. of manganous acetate to enter the structure of the charcoal after which the final adsorption of 15 lbs. of furfural to the charcoal is carried out. A steel article of low carbon steel measuring 8 inches in length, 4 inches in Width and 2% inches in thickness may be placed into a standard carburizing box having a capacity of 1 cubic feet together with the particles of the above carburizing 9 material which is packed around and about the steel article requiring 35 lbs. for the charge. After closing the carburizing box and luting the cover with clay, as is usually done in the ant, the carburizing box is introduced into a heat treating furnace and heating to a tempera ture of 1640 F. applied for a p'eriodof four hours to cause the formation of a case of carbonof one millimeter penetration into the steel surface of the steel article. The furnace shall be equipped with controllable heating devices to assure proper heat application. After cooling the furnace to the neighborhood of 1325" F., the carburizing box is removed and opened and the steel article taken out and permitted to undergo any further treatment desired but not within the scope of this invention, e.g. to quenching, whereas the depleted charcoal is removed and immediately readsorbed with a new charge of carburizing agent for reuse. The originally 35 lbs. of carburizing charge has lost approximately /2 lbs. of its weight, which includes loss of carbon dioxide formed from the sodium carbonate originally present. However, there is no need to replace this carbonate since usually sufficient energizer is still present after the first charge. Nevertheless, this may be also replaced by readsorption, so that to the depleted material, collected to be 100 lbs., readsorption may be performed in the same way as adsorption had been carried out in the first place. The readsorbed material is then again ready for use.

EXAMPLE 5 In another example, the furane derivative may be the sole adsorbed carburizing agent adsorbed to an adsorbent camier material such as a ceramic, e.g. alumina, which is reusable by virtue of its readsorption capacity after being depleted of its original carburizing charge. Thus, to 100 lbs. of activated alumina in the form of balls of 4'' diameter or from A1" to diameter sizes are added 41 lbs. of furfural under simultaneous cooling of the container in which the addition is made. The cooling is necessary on account of the great heat which develops during the adsorption of furfural to activated alumina. The resulting material is the carburizing material of the invention and, in this state, ready for use by packing the same around and about a steel article of a size 6 inches square and 3 inches thick placed into a carburizing pot of a size of 1 cubic foot. It is found that 40 lbs. of this carburizing material constitute the charge for this size carburizing pot, which is thereafter sealed with clay and placed into a temperature-controlled heating furnace, e.g. of the pusher type, for the desired carburizing treatment appropriate to the low carbon steel employed. Heating the charge to 1640" F. for a period of 4 hours causes a carbon case formation of a depth of one millimeter into the surface of the steel, after which the furnace is cooled to 1325 F. and the carburizing pot removed from the furnace and opened and the steel article taken out from the pot to permit further treatment thereof not within the scope of this invention, e.g. quenching, whereas the depleted alumina is removed and subjected to readsorption of a new charge of carburizing compound, e.g. furfural, of which 16 lbs. had to be replaced as computed for the charge of 40 lbs. carburizing material which had lost 16 lbs. during the carburizing operation. The readsorbed carburizing material is again readied for use. 7

EXAMPLE 6 This example employs furfuryl alcohol as the sole active carburizing agent adsorbed to an adsorbent carrier material e.g. charcoal, which can be reused by virtue of its readsorbability property after being depleted of an original carburizing charge. Thus, to 100 lbs. of charcoal in comminuted form of particles sized from A" to /8" diameter are adsorbed 23 lbs. of furfuryl alcohol.

invention and is packed item aaramumi a steel article placed into a carburizing box of 1 cubic foot capacity.

The steel article is of a size measuring 7 inches in length; 4 inches in width and 5 inches thick and of a low carbon steel type. The charge of carburizing material is 35 lbs., and after closing the carburizing box and luting the same with clay and placing into a heating furnace of the pusher type, the same is heated to 1640" F. for a period of 4 hours. After cooling the furnace to 1325 F., the carburizing box is removed from the furnace and EXAMPLE 7 Another example employs furan as the sole adsorbed carburizing agent to an adsorbent carrier material, e.g. coke, which can be reused by virtue of its readsorbability after being depleted of its original charge during carburizing operations. Thus, to 100 lbs. of coke in a comminuted form, e.g. of a size between A" and diameters, are adsorbed 12 lbs. of furan. The resulting material is the carburizing material of the invention and is packed around and about a steel article of low 'carbon steel placed into a carburizing box of 1 cubic foot capacity; The steel article, being of 8 inches in length, 4 inches in width and 3 inches thick, is surrounded by 30 lbs. of the carburizing material and the box luted with clay and thereafter placed into the heating furnace for heating to carburizing temperatures. of 1-640 F. for 4 hours to cause a carbon case formation of one millimeter depth into the surface of the steel article. After cooling the furnace, the carburizing box is removed and opened and the carburized steel article is taken out from the box for further treatment not within the scope of the invention, e.g. quenching, whereas the depleted carburizing material is again subjected to adsorption of a new charge of carburizing agent, e.g. to the readsorption of 3 lbs. of furan to 27 lbs. of the coke which had been recovered. The readsorbed carburizing material is again readied for use.

EXAMPLE 8 suitably comminuted particle size, e.g. inch to inch diameters, are adsorbed 12 lbs. of furfuryl acetate.

The resulting carburizing material is then packed about and around a steel article of low carbon steel placed'into a carburizing box of one cubic foot capacity. The steel article, being of a size 5 inches Wide, 6 inches long and of 4 inches depth, is packed in 30 lbs. of the carburizing material and the carburizing box is luted with clay before being placed into a temperature-controlled heating a furnace of a conventional type used in hardening operations in the art, and heated therein for 4 hours to a temperature of 1640 F. After cooling the furnace to 1325 F., the carburizing box is removed and opened and the steel article taken out for further treatment not within the scope of the invention, e.g. quenching, where- I as the depleted carburizing material, which has lost 3 lbs. of its weight, and is in the dry condition, is imme-' diately readsorbed with a new charge of carburizing compound, e.g. 3 lbs. of furfuryl acetate, and again ready for use. The depth of case obtained was one millime- The resulting ,materialis thecarburizing material of the ter. a

EXAMPLE 9 This example represents a carburizing material in which furoic acid is the sole carburizing agent adsorbed to charcoal as the inert carrier material for the same, which can be reused by virtue of its inherent readsorbability following depletion of its carburizing agent through use in carburizing operations. Thus to 100 lbs. of charcoal of a suitable size, e.g. A1 to inch in average diameters, is added 100 lbs. of a 25% solution of furoic acid in water at a temperature of between 90 and 100 F. and permitted to adsorb. The adsorption is speeded by slowly evaporating the water from the furoic acid solution under slightly heating the same, e.g. to 120 F., and drying, leaving the solid furoic acid within the porestructure of the charcoal. The dry material is ready for use and is packed about a steel article placed into a carburizing pot. The steel article constitutes a gear of 6 inches length and 12 /2 inches diameter for which a pot of appropriate shape with a capacity of one cubic foot is employed. The type of steel used is a low carbon type. The charge of carburizing material weighs 35 lbs. After closing the carburizing pot with clay and placing same into a heating furnace, a temperature of 1640 F. is employed for a period of four hours to obtain a case depth of one millimeter penetration into the surface of the steel article which is removed from the carburizing pot after cooling to 1325 F. and subjected to further treatments not within the scope of the invention, e.g. quenching. The depleted carburizing material remaining in the carburizing pot, after removal of the steel article, weighs approximately 27 lbs. because of the loss of its charge of approximately 8 lbs. of furoic acid during the carburizing operation, which can be replenished by repeating the adsorption procedure for the original adsorption and is thereafter again ready for use in carburizing operations.

EXAMPLE 10 This example employes a furane derivative as the carburizing agent, e.g. furfural, adsorbed to a carrier material together with a catalytic agent for the low temperature decomposition of the furane derivative, e.g. furfural, in which the carburizing carrier material is a ceramic, e.g. activated alumina. Thus, to 100 lbs. of activated alumina are adsorbed 10 lbs. of a 10% solution of nickelous acetate in water and dried. This is followed by adsorption of 41 lbs. of furfural, and the resulting carburizing material is then packed about and around a metal article of low carbon steel measuring inches in length, 4 inches in Width and 4 inches in height which is placed into a carburizing box of 1 cubic foot capacity and heated, after transferring the carburizing box to a heating furnace, for four hours to a temperature of 1640 F. A case of one millimeter depth of carbon penetration into the steel was obtained. After cooling the furnace to 1325 I and removing the carburizing box from the heating furnace, the steel article is taken out and subjected to further treatments not Within the scope of the invention, e.g. quenching, whereas the depleted carburizing material is readsorbed with a new charge of furfural for further reuse. As the charge consisted of 40 lbs. carburizingmaterial, from which 12 lbs. were used as same constituted the content of furfural, 12 lbs. furfural were used for readsorption to 28 lbs. of depleted alumina material con taining still catalyst adsorbed thereto in the active state.

EXAMPLE 1 1 Another example employs a furane derivative, e.g. furfural as carburizing agent adsorbed to coke as carrier materialtogether with a catalytic agent for the low temperature decomposition of the furane derivative, e.g. nickelous acetate. Thus,to 100 lbs. of coke are first added 5 lbs. of nickel acetate solution in water of a strength and permittedto be adsorbed and dried. This is followed by adsorption of 12 lbs. of furfural. The resulting material is the carburizing material of the invention and packed about and around a metal article of low carbon steel that is placed within the space provided by a standard carburizing pot'of 1 cubic foot capacity. The steel article measures 6 inches in length, 4 inches in width and 3 /2 inches in depth. After luting the carburizing pot with clay, its charge of 30 lbs. of carburizing material packed around the steel article is heated to 1640 F. for four hours in, a suitable heating furnace, e.g. of the pusher type into which the carburizing pot has been placed. After cooling to 1325 F, the carburizing pot is removed from the heating furnace and the steel article, possessing now a one millimeter carbon case, removed for further treatments not within the scope of the invention, e.g. quenching, whereas the depleted carburizing material is recovered for readsorption of a new charge of carburizing compound facilitating its reuse, in this instance by readsorption of 3 lbs. of furfural which is the amount of carburizing agent lost during carburizing operations.

EXAMPLE 12 This example represents a carburizing material containing adsorbed furfural as carburizing agent and adsorbed nickelous acetate as catalyst for the low temperature decomposition of the furfural that is contained in the carrier material for adsorption, e.g. charcoal in pellets measuring from A to inch in diameters. Thus, to lbs. of charcoal are adsorbed 25 lbs. of a 5% solution of nickelous acetate in water and dried. This is followed by adsorption of 22 lbs. of furfural. The resulting material is the carburizing material of the invention. This is packed around and about an article of low carbon steel of a size 9 inches long, 4 inches wide and 3 inches in thickness that is placed into a carburizing box of 1 cubic foot capacity, requiring 35 lbs. of carburizing material for its charge. After closing the carburizing box and luting its seams with clay, the box is placed into a heating furnace, e.g. of the pusher type, and heated therein at 1640 F. for a period of 4 hours to obtain a case of one millimeter depth of carbon penetration into the surface of the steel of the metal article being carburized. After cooling the furnace to 1325 F., the carburizing box is removed therefrom and opened and the steel article taken out for subsequent treatments not subject within the scope of the invention, e.g. quenching, whereas the depleted carburizing material is recovered for readsorption of a new charge of carburizing agent, e.g. furfural', in this instance 7 lbs. of furfural which is the amount lost during carburizing operations. The readsorbed carburizing material is again ready for use.

EXAMPLE 13 In carburizing an article of low alloy steel measuring, e.g. 7 inches in length, 4 inches in width and 3 /2 inches in depth, this article is placed into a carburizing box, e.g. of 1 cubic foot capacity, together with the carburizing material of the invention prepared by the adsorption of a furane derivative serving as carburizing agent, e.g. furfural in admixture with furan, to an inert ceramic carrier material, e.g. activated alumina, to which is co-adsorbed a catalyst agent for the low temperature decomposition of the furane derivative or mixture of derivatives, e.g. nickelous acetate, and a carburizing accelerating agent, e.g. molybdic acid. Thus, to 100 lbs. of activated alumina are adsorbed 10 lbs. of a 15% solution of nickelous acetate in water and dried. This is followed by adsorption of 10 lbs. of a 3% molybdic acid solution in hot water and dried again, to be finally followed by adsorbing 39 lbs. mixed furane derivatives. The resulting material is the carburizing material of the invention. This is packed about the steel article to be carburizing in form of a charge amounting to 40 lbs. of carburizing material. After closing the carburizing box and sealing the same with clay, the carburizing box is placed into a controlled temperature heating furnace, e.g. of the pusher type, and heated therein to.a.temperature of 1675 F. for one hours 13 time, which causes the formation of a case of .7 millimeter by virtue of the high concentration of carbon monoxide present from the charge of the super-active carburizing compound. This one hours high temperature treatment is followed by reducing the temperature to 15 F. for further three hours of treatment time to cause the formation of a desirable broadened zone of carburized steel surface of uniform hardness that slowly abates towards the core of the steel article and avoids the development of undesirable grain growth phenomena with a minimum warpage. After cooling the furnace to 1325 F., the carburizing box is removed therefrom and the steel article taken out for any further treatments not within the scope of the invention, e.g. quenching, whereas the depleted carburizing material is collected and readsorbed by a new charge of mixed furan derivatives, e.g. furan and furfural, and is then ready for reuse. For the lost charge from use in carburizing operation, 11 lbs. are readsorbed, which is equivalent to the amount of mixed furane derivatives lost, the original charge of 39 lbs. furane derivative to 100 lbs. of activated alumina consisting, for instance, of 3.9 lbs. of furan to 35.1 lbs. of furfural or 10% of the furfural.

EXAMPLE 14 In another example, a mixture of furane derivatives, e.g. furfural and furfuryl alcohol, are adsorbed to an adsorbent carrier material, e.g. coke together with a catalytic compound, e.g. cobaltous acetate, and a carburization accelerating agent, e.g. manganese trioxide and this carburizing material packed about and around a steel article in a carburizing box and heated therein to carburizing temperatures of a desired length of time that is appropriate with the desired case depth of carbon penetration. Thus, to 100 lbs. of coke are adsorbed a lbs. quantity of an aqueous solution of 5% manganous trioxide and dried. This is followed by adsorption thereto of a 5 lbs. quantity of an aqueous solution of cobaltous acetate and dried, and the final adsorption of 12 lbs. of a mixture of furfural and furfuryl alcohol, consisting of, e.g. 4 lbs. of furfural and 8 lbs. of furfuryl alcohol. The final material is the carburizing material of the invention, which is packed about and around the steel article of low carbon steel, of a size 10 inches long and in form of a roll with a diameter of 6 inches. After closing the carburizing box and placing the same into a heating furnace, heat is applied at a temperature of 1640 F. for 4 hours to obtain a case of 1 millimeter carbon depth into the surface of the steel. The furnace is thereafter cooled to 1325 F. and the carburizing box removed therefrom, followed by the opening of the box and subsequent removal of the steel article for subjecting the same to any further treatments, e.g. quenching, which to describe are not necessary as they are not within the scope of the invention. However, the depleted carburizing material is recovered and readsorbed by a similar charge of mixed furane derivatives to replace the :lost carburizing agent. The readsorbed material is again ready for use. The amount of lost carburizing agent is 3% lbs. because the employed charge for the oarburizing box amounted to 30 lbs. of carburizing material.

EXAMPLE 15 A final example represents the employment of a mixture of furane derivatives as carburizing agents adsorbed to an inert carrier material, e.g. charcoal, and the use therein of a catalytic compound that acts to decompose the furane derivatives at relatively much lower temperature than usual during carburizing operations perfomed on articles of steel, e.g. of a variety of shapes and sizes thereof, that are placed into a canburizing box for carburizing treatments thereto, and the further use in a carburizing material of a carburization accelerating agent. Thus, to lbs. of charcoal of a suitable pelleted size, e.g. from A1 inch to /8 inch in diameters, are adsorbed 25 lbs. of a 5% nickel acetate solution in water and dried. This is followed by adsorption thereto of 15 lbs. of a 10% solution of manganous heptoxide in water and drying, and final adsorption thereto of a mixture of furane derivatives consisting of 5 lbs. of furan, 10 lbs. of furfural and 5 lbs. of fur-furyl alcohol. The final material is the carburizing material of the invention, which is packed around and about an article of low carbon steel measuring 8 inches length of a square bar of 4 inches diameter diagonally, that is placed into a carburizing box of 1 cubic foot capacity, in form of a charge of 35 lbs. carburizing material. After closing the carburizing box and inserting the same into a heating furnace of suitable size, e.g. a pusher type conventional furnace, heat is applied to the charge for 4 hours at 1640 F. After cooling the furnace, the carburizing box is removed therefrom and opened as the temperature reaches 1325 F. and the steel article taken out from the box for further treatments not a part of this invention, e.g. quenching, whereas the depleted carburizing material is collected for readsorption thereto another similar charge of carbuzizing agent, e.g. 6 /2 lbs. of the employed mixed furane derivatives, e.g. comprising by weight 25% furan, 50% furfural and 25 furfuryl alcohol, after which the readsorbed carburizing material is again ready for use. The case obtained in the steel surface of the article being treated was found to be 1.1 millimeters in depth.

With the above detailed disclosure of the invention, it is evident that numerous modifications will suggest themselves to those skilled in the art and it is not desired to limit the invention to the exact uses and examples disclosed.

What I claim is:

1. In the method of hardening metal articles made of iron, steel, and alloys thereof, in a chamber heated to the canburizing temperature, the step of carburizin-g the metal articles in the presence of a decomposable furane derivative, for sufiicient time to decompose the furane derivative into carburizing gases and to carburize the metal articles to the desired depth of hardening.

2. In the method of claim 1, wherein the furane derivative is fur-fural.

3. In the method of claim 1, wherein the furane derivative is fur-furyl alcohol.

4. In the method of claim 1, wherein the furane derivative is furfuryl acetate.

5. In the method of claim 1, wherein the furane derivative is furan.

6. In the method of claim 1, wherein the furane derivative is furoic acid.

References Cited in the file of this patent UNITED STATES PATENTS 1,432,416 Rodman Oct. 17, 1922 1,742,791 Somerville' Jan. 7, 1930 1,893,368 Hogaboom Jan. 3, 1933 OTHER REFERENCES Steel Processing, July 1953, pages 335-339 and 349, by Hyler.

Metals Handbook, 1948 edition by American Society for Metals. Pages 686688. 

1. IN THE METHOD OF HARDENING METAL ARTICLES MADE OF IRON, STEEL, AND ALLOYS THEREOF, IN A CHAMBER HEATED TO THE CARBURIZING TEMPERATURE, THE STEP OF CARBURIZING THE METAL ARTICLES IN THE PRESENCE OF A DECOMPOSABLE FURNANE DERIVATIVE, FOR SUFFICIENT TIME TO DECOMPOSE THE FURANCE DERIVATION INTO CARBURIZING GASES AND TO CARBURIZE THE METAL ATICLES TO THE DESIRED DEPTH OF HARDENING. 